matryce i terabajty...

In old Sup720 design, the Supervisor itself is connected to the fabric using one channel. This channel is used by Hyperion ASIC to provide for bus interface, and multicast/SPAN features. Because there's no other way to connect the uplinks on the Sup itself, the Hyperion has it's interface also terminating the uplinks (2xGE) thus limiting effective throughput/etc. BTW, both PFC and MSFC are also connected to the rest of the chassis linecards by Hyperion (PFC) and Pinnacle (MSFC).

On the Sup720-10GE, the separate, 19th channel is used to connect the uplinks directly into fabric. Hyperion is still there, it still takes the channel "belonging" to the slot which Supervisor itself is in, but thanks to such design doesn't limit in any way performance you can achieve on the 2x10GE uplinks (or 4xGE). In the new design, Hyperion takes care of providing connectivity to MSFC3 complex, while Metropolis (ASIC terminating the uplinks and connected to fabric) takes care of providing transport to PFC3C/CXL.

The 20th channel is used in the same fashion for the redundant Sup if it's inserted into chassis.